Beat detection is one feature used in implantable cardiac stimulation devices. Accurate beat detection is important to ensuring device success. For example, with an implantable cardioverter/defibrillator (ICD), inaccurate beat detection can lead to unnecessary stimulus and/or failure to provide stimulus when needed.
FIG. 1, taken from Ellenbogen et al. in CLINICAL CARDIAC PACING AND DEFIBRILLATION 2ND Ed. (W.B. Saunders Co. 2000), at 201, shows that the frequency content of raw cardiac signals includes various components. T-waves typically have low frequency content below 10 hertz. Myopotentials from non-cardiac muscles tend to have higher frequency content, in the range of 80 hertz and above. P-waves, which tend to be discarded or considered undesirable, appear at frequencies in the 30-60 hertz range. R-waves, which are often used as the benchmark for beat detection, have frequency content in the range of 20-40 hertz.
Making detection more difficult is the fact that the cardiac conditions which an implanted device must accurately detect are abnormal conditions. In particular, various tachyarrhythmia conditions may occur. Some, but not all, tachyarrhythmia conditions are malignant. In some morphologies, R-waves become difficult to discern, particularly with automated detection techniques. Improvements allowing for better detection, particularly during tachyarrhythmia conditions, are desired.